GIFT  OF 


No.  1668 


■  DESCRIPTION 

M  OF  THE 

DEFLECTION   BOARD 

(MODEL  OF  1906) 
WITH  DE  CARRE  DRIFT  CHART 

FOR  12 -INCH  MORTAR 

MECHANICAL  FEATURES, 

RULES  GOVERNING  ITS  CARE,  OPERATION, 

AND  PRESERVATION  IN  SERVICE 


{ONE  PLATE) 


APRIL  4,  1907 

REVISED  DECEMBER  13,  1907 

REVISED  JULY  2,  1917 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1917 


No.  1668 


DESCRIPTION 

OF  THE 

DEFLECTION   BOARD 

(MODEL  OF  1906) 
WITH  DE  CARRE  DRIFT  CHART 

FOR  12 -INCH  MORTAR 

MECHANICAL  FEATURES. 

RULES  GOVERNING  ITS  CARE,  OPERATION. 

AND  PRESERVATION  IN  SERVICE 

W  

{ONE  PLATE) 


APRIL  4,  1907 

REVISED  DECEMBER  13,  1907 

REVISED  JULY  2,  1917 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1917 


*'v    •  *»  .'^« 


<^  "  <  -J  A-»  »,  ft'  •  ''.»      «;  »  »  t '  t  "t,  *•.  *' 


War  Department, 
Office  of  the  Chief  of  Ordnance, 
Washington,  July  2,  1917, 
This  Manual  is  published  for  the  information  and  government  of 
the  Eegular  Army  and  National  Guard  of  the  United  States. 
By  order  of  the  Secretary  of  War. 

William  Crozier, 
Brigadier  General,  Chief  of  Ordnance, 

562-17  (3) 


365246 


7"Tn' 


DESCRIPTION  OF  THE  DEFLECTION  BOARD,  MODEL  OF  1906, 
WITH  DE  CARRE  DRIFT  CHART,  FOR  12-mCH  MORTAR. 

(1  Plate.) 


,  1.  The  deflection  board,  model  of  1906,  with  De  Carre  drift  chart, 
for  12-inch  mortar,  consists  of  a  built-up  wooden  base  of  cherry,  of 
mahogany  finish,  called  the  block,  to  which  is  secured  a  bronze 
frame,  supporting  the  cylinder,  the  shield,  the  De  Carre  drift  chart, 
main  traversing  screw,  and  wheels,  shown  in  the  deflection  board, 
assembled.  The  purpose  of  the  board  is  to  afford  a  means  of  de- 
termining rapidly  the  full  correction  in  azimuth  to  be  apphed  in  12- 
inch  mortar  firing.  This  pamphlet  will  discuss  the  mechanical 
features  of  the  instrument  and  its  operation,  care,  and  preservation. 
The  use  of  the  instrument  in  conjunction  with  the  other  instruments 
of  the  mortar  fire  control  and  direction  system  is  discussed  in  pub- 
Hcations  issued  by  the  Chief  of  Coast  Artillery. 

2.  The  construction  of  the  board  depends  upon  the  theory  that 
the  angular  drift  is  constant  for  a  given  elevation,  whatever  the  ve- 
locity. The  range  table  drifts  for  the  several  types  of  projectiles, 
including  2.95-inch  subcaliber,  for  elevations  from  45°  to  65°, are 
plotted  on  the  chart  and  a  change  from  one  type  of  projectile  to  the 
other  can  be  readily  made. 

3.  The  final  correction  given  by  the  board  as  the  result  of  any 
assumed  prior  conditions  as  to  elevation,  weight  of  projectile,  etc.,  is 
obtained  by  mechanically  setting  a  pointer  at  a  given  place  on  a 
graduated  scale  and  then  setting  a  second  graduated  scale  in  a  given 
position  with  reference  to  the  drift  chart.  The  corrected  azimuth 
is  then  indicated  by  a  second  pointer  and  graduated  scale.  The 
pointers  are  the  imcorrected  azimuth  pointer  marked  ''Set'^  and  the 
corrected  azimuth  pointer  marked  '^Read.''  The  scales  are  the 
azimuth  scale,  engraved  for  whole  degrees  on  the  cyhnder,  and  the 
azimuth  subscale  for  fractional  parts  of  degrees,  least  reading  5/100, 
on  the  frame,  and  the  adjusting  scale. 

4.  The  whole  degrees  of  the  azimuth  scale,  engraved  on  the  cylin- 
der, are  arranged  in  36  rows  of  figures  spaced  evenly  about  the  out- 
side of  the  cylinder  as  shown.  Each  row  begins  with  some  whole  de- 
gree number  terminating  in  the  number  1,  and  contains  altogether 
21  whole  degree  numbers.  An  inspection  of  the  cyhnder  will  show 
this  clearly.  The  reason  lor  engraving  the  whole  degree  numbers 
in  this  way  is  that  the  movements  of  the  various  pointer  slides  must 


necessarily  be  limited,  for,  if  for  any  reason  corrections  would  in- 
volve moving  the  slides  to  which  the  pointers  are  attached  so  far 
either  to  the  right  or  left  as  to  run  them  off  of  their  traversiag  mech- 
anisms, the  board  would,  temporarily  at  least,  be  out  of  commission 
and  further  rapid  work  would  be  prevented.  To  overcome  any  such 
possibility  stops  Hmiting  the  movement  of  all  sUdes  have  been  pro- 
vided. If,  therefore,  in  setting  any  of  the  pointers,  a  stop  is  en- 
countered, grasp  the  handle  and  ratchet  ring  on  the  left  end  of 
cylinder  and  move  the  azimuth  scale  on  cyUnder  either  forward  or 
backward  one  row  of  whole  degree  numbers,  depending  upon  whether 
the  stop  has  been  encountered  toward  the  left  extremity  or  right 
extremity  of  movement  of  any  of  the  slides.  For,  in  moving  toward 
the  left,  whole  numbers  on  the  scale  are  of  decreasing  value;  hence 
if  a  stop  is  encountered  on  the  left,  by  moving  the  cylinder  one  row 
forward  the  next  row,  10  whole  degrees  in  value  less  than  the  original 
row,  is  brought  to  the  reading  opening  under  the  guard,  and  the  ad- 
justment of  the  pointers  can  again  be  undertaken  by  running  all  to 
the  right  of  the  instrument  a  distance  equal  to  10  whole  degree 
spaces.  A  rapid  manipulation  of  the  pointer  is  provided  for  in  the 
pitch  of  the  various  operating  screws,  pinions,  and  racks. 

5.  It  should  be  noted  that  the  azimuth  subscale  of  fractional  parts 
of  degrees,  least  reading  5/100  degree,  is  stationary  and  does  not 
move  when  the  cylinder  is  revolved.  The  whole  degree  numbers  on 
the  cylinder  are  so  spaced  that  as  each  comes  opposite  the  reading 
opening  under  the  shield  it  is  situated  opposite  a  whole  degree  grad- 
uation on  the  fixed  part  of  the  azimuth  subscale  on  the  frame. 

6.  The  method  of  moving  the  cylinder,  containing  the  whole  degree 
numbers  of  the  azimuth  scale,  has  already  been  described.  The  other 
movements  of  the  board  affect  directly  the  position  of  the  pointers, 
and  will  now  be  described.  Examining  the  assembled  view  of  the 
deflection  board,  there  will  be  seen  on  the  extreme  right  a  handwheel, 
called  the  main  traversing  wheel.  This  wheel  is  attached  to  the 
right  end  of  the  main  traversing  screw.  The  main  traversing  screw 
is  a  double  screw,  of  square  thread  and  rapid  pitch,  passing  through 
the  carriage,  and  traversing  the  latter  right  or  left.  As  the  carriage 
supports  all  pointers  of  the  board,  either  directly  or  by  attachment, 
all  pointers  must  move  together  when  the  main  traversing  screw  is 
operated  to  traverse,  and  during  such  movement  all  pointers  will 
retain  their  relative  positions.  In  other  words,  the  main  traversing 
screw  is  operated  only  to  set  the  uncorrected  azimuth  pointer  marked 
"Set"  at  the  desired  angle  on  the  azimuth  scale.  The  corrections  for 
drift  or  deflection  are  not  affected  by  operating  the  main  traversing 
screw. 

7.  Directly  below  the  azimuth  subscale  is  the  carriage,  which 
affords  a  seat  for  the  slide.     The  carriage  is  moved  left  or  right  by 


turning  the  main  traversing  wheel.  The  uncorrected  azimuth  poin- 
ter, which  is  enameled  red  and  marked  ''Sef  in  white  letters,  is 
attached  to  the  carriage  and  is  provided  to  enable  the  instrument  to 
be  set  to  the  uncorrected  azimuth  on  the  subscale. 

8.  The  slide,  upon  which  is  mounted  the  drift  chart  mechanism,  is 
moved  left  or  right,  independently  of  the  carriage,  by  rotating  the 
slide  knob.  Located  at  each  end  of  this  slide  are  bearings  provided 
for  the  front  and  rear  rollers.  The  notches  cut  in  the  front  boss  of 
the  right  bearing,  form  seats  for  the  teeth  of  the  front  bearing  clutch. 
The  corrected  azimuth  pointer,  which  is  enameled  white  and  marked 
''Read''  in  red  letters,  is  secured  to  the  slide. 

9.  The  drift  chart  mechanism  consists  principally  of  the  front  and 
rear  rollers,  the  drift  chart  and  the  adjusting  scale.  The  principal 
parts  of  the  rear  roller  are  the  rear  rod,  chart  clamp,  knob,  knob  fric- 
tion spring,  and  clamp  knob.  The  rear  roller  is  designed  to  carry  the 
drift  chart,  which  may  be  wound  up  on  the  rod  by  turning  the  rear 
rod  knob.  The  knob  friction  spring  provides  friction  to  overcome 
the  tension  in  the  spring,  which  is  located  inside  the  front  roller  and 
prevents  any  movement  of  the  chart  imder  the  action  of  the  spring. 
An  adjustment  is  provided  for  the  knob  friction  spring  by  means  of 
the  nut  securing  the  rear  rod  knob  to  the  rear  rod.  The  rear  rod 
clamping  device  is  provided  for  holding  the  chart  against  accidental 
displacement  during  firing.  This  device  consists  principally  of  the 
clamp  knob,  clamp  screw,  and  clamp  bushing. 

10.  The  front  roller  is  made  up  of  a  hollow  tube,  inside  of  which  is 
located  a  spiral  spring,  of  a  chart  clamp  tube  and  the  front  bearing 
clutch.  One  end  of  the  spring  is  attached  to  the  roller  and  the  other 
to  the  front  bearing  clutch,  so  that  an  adjustment  of  the  spring  tension 
may  be  obtained  by  turning  the  clutch.  A  screw  in  the  end  of  the 
clutch  is  provided  for  hoiding  the  ciutch  teeth  engaged.  This  should 
be  loosened  when  it  is  desired  to  adjust  the  spring  tension.  Care 
should  be  taken  not  to  allow  the  front  bearing  clutch  to  slip  from  the 
jBngers  after  the  teeth  have  been  disengaged  since  this  is  liable  to 
break  the  spring, 

11.  The  adjusting  scale  is  secured  to  the  left  end  of  the  carriage 
by  two  dowel  pins  and  three  screws.  A  slight  longitudinal  adjust- 
ment is  provided  for  this  scale  to  accommodate  it  to  the  drift  chart 
if  necessary.  'The  scale  is  graduated  1.50°  on  either  side  of  the  index 
pointer  or  normal,  which  is  indicated  by  the  figure  *'3."  The  least 
reading  is  5/100  degree,  the  same  as  that  of  the  azimuth  subscale. 
This  scale  corresponds  to  the  lateral  drift  scale  in  the  battery  com- 
mander's instrument  and  is  used  on  the  deflection  board  in  making 
corrections  for  lateral  deviations. 

12.  The  method  of  operating  the  various  screws,  handles,  and 
knobs  has  now  been  described  in  detail.     To  group  movements — 


8 

that  is,  to  make  drift  and  deflection  correction  at  the  same  time — it 
will  not  affect  the  result  if  either  of  the  corrections  is  made  first  or 
last.  In  other  words,  the  final  answer  is  not  affected  if  the  drift  cor- 
rection is  made  before  the  deflection,  or  \dce  versa. 

13.  All  exposed  metal  surfaces  of  this  instrument,  except  wearing 
surfaces,  are  given  a  sand-blast  finish,  covered  with  a  coat  of  trans- 
parent lacquer.  Graduations,  figures,  and  letters  are  filled  in  with 
black.  The  parts  of  the  instrument  subject  to  friction,  as  trunnion 
bearings,  translating  screws,  etc.,  should  be  oiled  with  clock  oil  when 
necessary.  Where  parts  are  not  readily  accessible  for  oiling,  oil 
holes  have  been  provided.  An  excess  of  oil  should  not  be  used. 
Should  an  oil  spot  or  mark  develop  on  any  part  of  the  board  having 
the  sand-blast  finish,  it  may  be  readily  wiped  off,  using  a  cloth  and 
a  Httle  soap  and  water.  The  place  should  be  thoroughly  dried  after 
cleaning  and  a  thin  coat  of  transparent  lacquer  applied  if  the  original 
covering  was  removed  during  the  operation  of  cleaning.  If  no 
lacquer  is  available,  a  thin  coat  of  machine  oil,  evenly  appHed,  may 
be  used  temporarily. 

OPERATION  OF  THE   BOARD. 

14.  Turn  the  handle  and  ratchet  ring  until  the  proper  degree  on 
the  cylinder  is  brought  into  view,  set  the  uncorrected  azimuth 
pointer  marked  ''Set,"  to  the  uncorrected  azimuth  of  the  set-forward 
point  by  turning  the  main  traversing  wheel.  Set  the  drift  chart  to 
the  normal  for  the  projectile  being  used,  by  rotating  the  rear  rod 
knob,  then  clamp  the  rear  roUer  by  tightening  up  on  the  clamp  knob. 
The  correct  position  is  indicated  when  the  fiducial  edge  of  the  ad- 
justing scale  coincides  with  the  horizontal  line  on  which  the  type  of 
projectile  to  be  used  is  marked.  Set  the  normal  or  index  pointer  of 
the  adjusting  scale  to  the  elevation  determined  from  the  range  ele- 
vation board,  by  turning  the  slide  knob.  The  corrected  azimuth  is 
then  indicated  under  the  corrected-azimuth  pointer  marked  ''Read." 
This  pointer  then  indicates  the  corrected  azimuth  of  the  set  forward 
point  for  the  elevation  and  type  of  projectile  used. 

METHOD    OF    MAKING    CORRECTIONS    FROM    INSTRUMENTAL 
OBSERVATION   OF  FIRE. 

15.  Corrections  may  be  made  for  latter al  deviation  from  the  in- 
striunental  observation  of  fire  as  follows:  First,  note  from  the  battery 
commander's  instrument  the  point  of  fall  of  the  splash,  that  is,  the 
reading  of  the  splash,  taken  with  reference  to  the  target  on  the  lateral 
deviation  scale  of  the  battery  commander's  instrument.  Assume 
the  splash  to  fall  on  this  scale  at  2.75  or  .25°  right.  Note  the  ele- 
vation at  which  this  shot  was  fired.  Loosen  the  clamp  loiob,  then 
by  means  of  the  rear  rod  knob,  turn  the  drift  chart  until  the  eleva- 


9 

tion  line,  for  the  elevation  at  which  the  shot  was  fired,  coincides  with 
reading  2.75  on  the  adjusting  scale,  then  again  tighten  the  clamp 
knob.  The  drift  chart  has  thus  been  moved  from  normal  a  sufficient 
amount  to  correct,  at  the  elevation  at  which  the  shot  was  fired,  for 
the  lateral  deviation  of  25°  right,  and  this  correction  will  be  applied 
in  the  same  ratio  as  the  normal  drifts  are,  for  all  other  elevations 
between  45°  and  65°. 

16.  When  ordering  spare  parts,  use  the  following  nomenclature, 
etc.: 


Name  of  part. 


Adjusting  scale . 

Bearing 

Block 

Carriage 

Cap. 


Cap  screw 

Cylinder 

Cylinder  end,  left 

Cylinder  end,  right 

Chart  clamp 

Clamp  bushing 

Clamp  knob 

Clamp  screw 

Corrected  azimuth  pointer 

Frame 

Front  right  bearing 

Front  left  bearing 

Front  bearing  clutch 

Front  bearing  clutch  screw 

Front  inner  tube 

Handle  and  ratchet  ring 

Knob 

Knob  stud 

Knol)  friction  spring 

Main  traversing  screw 

Main  traversing  screw  collar 

Main  traversing  screw  washer 

Main  traversing  wheel 

Name  plate '. 

Plunger 

Plunger  spring 

Rack 

Rear  rod .^ 

Rear  rod  knob-.T 

Rear  rod  nut 

0.123  by  0.312  (^)  round-head  screws.. 

0.123  by  0.375  headless  screws 

0.125  by  0.14  countersunk-head  screws. 

0.123  by  0.25  filister-head  screws 

0.189  by  0.375  round-head  screws 

0.06  by  0.12  iilister-head  screws 

0.125  by  0.1  filister-head  screws 

0.125  by  0.22  iilister-head  screws 

Shield 

Slide 

Slide  knob 

Slide  fjinion 


Piece 
mark. 


4C. 
3F. 
3D. 
4A. 
3E. 
3G. 


2A. 
2G. 
2E. 
5E. 
4G. 
4E. 
4F. 
4P. 
3A. 
5Q. 
5L. 
5R. 
5S.. 
5K. 
2H. 
2Q. 
2L. 
5D. 
2K. 
2W. 
2U- 
2P. 
3C.. 
2R. 
2S.. 
3B. 
5A. 


5B 

5C.. 
2M. 
2F. 
4K. 
2B. 
2C.. 
5M. 
4B. 
4D. 
2N. 
4M. 
4R. 
4L. 


Dra^^dng 
No. 


-50-4 
-50-3 
-50-3 
-50-4 
-50-3 
-50-3 
-50-2 
-50-2 
-50-2 
-50-5 
-50-4 
-50-4 
-50-4 
-50-4 
-50-3 
-50-5 
-50-5 
-50-5 
-50-5 
-50-5 
-50-2 
-50-2 
-50-2 
-50-5 
-50-2 
-50-2 
-50-2 
-50-2 
-50-3 
-50-2 
-50-2 
-50-3 
-50-5 
-50-5 
-50-5 
-50-2 
-50-2 
-50-4 
-50-2 
-50-2 
-50-5 
-50-4 
-50-4 
-50-2 
-50-4 
-50-4 
-50-4 


10 


Name  of  paxt. 


Piece 
mark. 


Spring 

Spring  guide 

0.093  {^)  by  0.812  (H)  taper  pin 

0.062  (Vj)  by  0.5  taper  pin 

0.093  (^)  by  0.43  taper  pin 

Uncorrected  azimuth  pointer 

Washer 

Washer 

Washer 


Drawing 
No. 


22-50-5 
22-50-5 
22-50-2 
22-50-4 
22-50-4 
22-50-4 
22-50-5 
22-50-5 
22-50-5 


War  Department, 

Office  of  the  Chief  of  Ordnance, 

Washinglon,  July  2,  1917. 
April  4, 1907. 
Revised  Dec.  13, 1907. 
Revised  July  2, 1917. 
38766-27-1. 

062.1/2227,  Rev.  No.  1668. 
Form  No.  1668. 
Ed.  July  2-17-1,500. 
[No.  1668] 


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UNIVERSITY  OF  CAUFORNIA  LIBRARY 


